26th (2:00-5:00PM) November, 2013

R. S. Myong

Dept. of Aerospace and System Engineering

Aerospace Computational Modeling Lab; http://acml.gnu.ac.kr

Gyeongsang National University, South Korea

myong@gnu.ac.kr

Presented at KAI

Establishing Computational Simulation Capability for Aircraft Lightning Certification 항공기 낙뢰 해석 및 인증 기술

Acknowledgement of

Dr. Sangwook Lee (Boeing)

R. Ranjith (GNU; Graduate Student)

and

financial support through the Brain Pool program.

Subjects

• Introduction of lightning

Lightning research communities and references

Aircraft lightning and its importance

• Lightning certification

Certification process and standards

Current waveforms

Lightning zoning

Steps in protection design and certification

• Computational lightning simulation

Role of computational simulation and applications

Numerical codes

Mechanical-thermal-electrical physical modeling

Validation of computational codes

Subjects (Continued)

• Sample calculations

Integrated wet fuel tank

EM simulation supporting lightning protection design

• Recent research trend

New zoning method

Digital photographic technique

Conductivity in composites and scaling issues

Lightning research using UAV

• Summary

Major computational capabilities and issues

• Q & A

Research Communities and References

• ICOLSE International Conference on Lightning and Static

Electricity (Seattle 2013; www.icolse.us, 2007)

• Aircraft lightning requirements, components testing,

aircraft testing, and certification (University of Kansas

Course, 2012); introduction, EMI EMC, certification,

environment, aircraft lightning attachment phenomena,

lightning effects on aircraft, direct effect, indirect effect,

design to minimize indirect effects, fuel systems, aircraft

wiring

• Lightning hazards of aircraft and launchers, Journal

Aerospace Lab (12 articles, Issue 5, December 2012)

• Other journal articles

Lightning - Importance

• Lightning is an atmospheric electrical phenomenon which deserves adequate protection design of aircraft.

• Though the probability of the lightning strike is very low (10-9 events per hour), the effects might be quite considerable. (small-size solid-state components, sensitive devices, reinforced polymers, complex systemization → Lightning protection must be considered from the start. Cf. Embedded de-icing systems)

Lightning – Importance (Korea)

Lightning – Effects

• The effects of lightning are classified into two as direct

and indirect effects.

• Direct effects include the structural damage, fuel ignition,

etc., whereas indirect effects are interference to the

navigation equipment.

• The worst case would be the loss of the aircraft and the

lives in it.

Lightning – Mean Rate

• Pan Am Boeing 707 in 1963: induced EM effects in the fuel tank

• Iran Air Boeing 747 in 1976: arcing in the fuel tank by a direct lightning strike

• TW800 in 1996: central fuel tank explosion (wear and tear on bonding braids and sparking at chafed wiring)

• Mean rate of one event per year

Lightning – Air France Case

1 2

3

6

7

4

5

1 2

3

6

7

4

5

• Strikes take place during: approach, cruise, take-off

• Damage locations

• Damage effects: – 68% minor – 24% moderate – 8% major (flight control planes)

• Air France: – 0.7 events/AC/year – 205 hrs delay, 11 flights cancelled

• Use of ILDAS (In-flight Lightning Strike Damage Assessment System) could result in more efficient maintenance procedures.

Lightning – Phenomenon

Generalized diagram

showing distribution of

air currents and

electrical charge in a

typical cumulonimbus

cloud

Lightning - Triggering/Interception

• Transall C160 research

aircraft (1980s)

Lightning - Triggering/Interception/Sweeping

Lightning – Typical Current Waveform

C160 research aircraft

Idealized high current

waveforms

Lightning - Certification

• Fundamental goal:

To prevent catastrophic accidents, and to enable the aircraft to continue flying safely and be able to land at a suitable airport.

• The lightning protection requirements have been included in the collection of Federal Aviation Regulations (CFRs) and Advisory Circulars (ACs).

• A certification plan needs to be submitted earlier in the certification process. It includes Description of the system

Description of the protection

Pass/Fail criteria

Lightning - Certification

CFRs Pertaining to Lightning Protection

Vehicle Type and Regulations

Aircraft Rotorcraft

General Aviation

Transport Normal Transport

Airframe 23.867 25.581 27.610 29.610

Fuel System 23.954 25.954 27.954 29.954

Other System

23.1306 25.1316 27.1316 29.1316

Lightning - Certification

Guidance Documents: EUROCAE & SAE

Lightning - Certification

• Aerospace Recommended Practice (ARP) edited by the

SAE international group: ARP 5412A (Waveforms), ARP

5414A (Zoning), etc.

• SAE ‘Blue Book’ “Lightning Test Waveforms and

Techniques for Aerospace Vehicles and Hardware.” The

US standard for aircraft protection design and

certification testing, of both civil and military aircraft.

Foreign certifying agencies accepted this standard via

bilateral agreements

Lightning - Certification

• SAE ‘Orange book’ “Protection of Aircraft Electrical/

Electronic Systems Against the Indirect Effects of

Lightning.” In wide use as a de facto standard for

certification of flight critical or essential systems aboard

transport category aircraft.

Lightning – Certification (Continued)

• AC 20-53 dealt exclusively with lightning protection of

airplane fuel systems.

• The Federal Aviation Regulation Part 23.945, fuel

system lightning protection reads:

The fuel system must be designed and arranged to prevent

the ignition of fuel vapor within the system by

(a) Direct lightning strikes to areas having a high

probability of stroke attachment;

(b) Swept lightning strokes on areas where swept strokes

are highly probable; and

(c) Corona or streamering at fuel vent outlets.

Certification Steps

• Determine the lightning strike zones

• Establish the lightning environment

• Identify flight critical/essential components

• Establish protection criteria: determine system/

components protected and establish pass-fail criteria

• Design lightning protection

• Verify protection adequacy by similarity with previously

proven designs, by simulated lightning tests or by

acceptable analysis. When analysis is utilized,

appropriate margins may be required to account for

uncertainties in the analytical techniques

Design Protection

• Direct effects: the basic structural material and

manufacturing techniques, the addition of treatments or

devices to improve electrical conductivity, arc or spark

suppression, finishes, sealants and gaskets, application

of lightning diverters, insulating structures and electrical

bonding provisions and relocation of equipment

• Indirect effects: application of electromagnetic shielding,

provision of low impedance grounding surfaces,

incorporation of surge suppressors and proper design of

input and output circuits of electronic equipment

Test Plans

• Purpose of the test

• Production or test article to be utilized

• Article configuration and test drawing

• Method of installation that simulates the production

installation

• Applicable lightning zone(s)

• Lightning simulation method; test voltage or current

waveforms

• Diagnostic methods

• Pass/fail criteria

• Appropriate schedule and location of proposed test

Test Procedural Steps

• Obtain FAA concurrence that the test plan is adequate.

• Obtain FAA concurrence on details of part conformity of

the test article and installation conformity of the test

setup.

• Schedule FAA witnessing of the test(s).

• Conduct testing.

• Submit a final test report describing all results.

• Obtain FAA approval of the report.

Concluding Remarks

• Need of further activities in lightning study

• Major computational capabilities required for future

program

- Zoning

- EM simulation of transient lightning physics

- Mechanical-thermal-electrical coupled simulation

Concluding Remarks (Continued)

• Main issues in computational simulation for structure

- Global/local current distribution

- Current distribution in fasteners (found randomness-

oscillation or focusing of current on one fastener)

- Damage effects in materials

- Sparking conditions/threshold

- Lightning protection of radomes (electro-static

approach is common; what shape beneath the skin is the

key factor)

Q & A